Perfumes or fragrances comprising fragrance molecules or components are utilized in various household products to improve the aesthetics associated with their use. Examples of products that contain fragrance molecules include deodorants, skin-care products, laundry detergent compositions (both liquid and granular), household cleaning compositions, fabric softeners, hair care products (including shampoos and conditioners), air fresheners, cosmetic preparations, and personal cleaning products (such as soaps and bath gels). The use of fragrances in such products is generally recognized as being essential for achieving consumer acceptance. However, fragrance molecules are generally highly volatile, especially the so-called “top notes” which are generally regarded as essential for delivering a “fresh” or “clean” odor to substrates, such as skin, hair or clothing. The highly volatile top notes of a perfume composition are typically lost during use, or even during storage, and especially upon prolonged heating, such as in a clothes dryer. Accordingly, there is a recognized need for releasing fragrance components, especially the more volatile top notes, at a controlled rate for various consumer products.
In the case of laundry detergent compositions, it is desirable to increase the amount of perfume carried over from an aqueous laundry or cleaning bath onto fabrics, and thereafter release the fragrance molecules at a controlled rate. Similarly, it is desirable to control the rate of release of fragrance molecules deposited on various substrate surfaces, such as hair and/or skin during use of personal cleansing compositions and/or hair-care products.
There have been various attempts to achieve controlled or sustained release of fragrance molecules from a variety of consumer products utilizing encapsulation techniques and/or pro-perfumes. Micro-encapsulation and inclusion complexes with specific materials such as cyclodextrins have been used to decrease volatility, improve stability and provide slow-release properties of perfuming ingredients. However, when contacted with an aqueous medium, cyclodextrin-based systems release the fragrance immediately, which limits their use as controlled release systems. Specifically, this characteristic limits the use of cyclodextrin encapsulation for most consumer products, including skin-care products, hair-care products, laundry detergent compositions, household cleaning compositions, personal cleansing products, etc., which are generally used in an aqueous environment, or at least in the presence of moisture. Other known encapsulation techniques, such as spray-drying, coacervation, and extrusion, are generally unsatisfactory for use in most consumer products, because they do not provide suitable substantivity on a substrate, i.e., an insufficient quantity of perfume ingredients are deposited and adhered on the substrate.
The use of perfume delivery systems comprising perfume molecules absorbed onto a polymeric carrier material has also been explored. While these systems provide an improvement of deposition of perfume in certain applications, these systems do not allow controlled release of the perfume over a prolonged period of time. Specially, most of the known fragrance delivery systems comprising perfume molecules absorbed on a polymeric carrier material release fragrance at a rate that is not significantly prolonged.
WO 2004/067584 discloses a perfume delivery system comprising perfume molecules absorbed onto micro-particles or nano-particles that have been modified at their surfaces to provide prolonged release of the perfume molecules, while also enhancing substantivity (i.e., adherence to a substrate). The particles are obtained by dispensing at least one hydrophobic monomer into a medium wherein the corresponding polymer is not soluble. The medium comprises an initiator, a cross-linking agent and at least one stabilizer to provide a suspension, dispersion or mini-emulsion. The medium is heated to induce polymerization and form spherical hydrophobic polymer particles. Optionally, un-reacted monomers are removed. A chemical agent capable of chemically modifying the particles to transform hydrophobic moieties into hydrophilic moieties at the surface of the particles is added. Fragrance molecules are then absorbed into the particles to provide a sustained perfume delivery system. However, the '584 publication discloses that purification in the preparation of the perfume delivery system is essential to avoid any un-reacted monomer from contaminating the perfuming ingredients.
There has also been considerable interest in research relating to the use of pro-fragrances, in which a fragrance molecule is reversibly associated (i.e., covalently bonded) with a carrier molecule to provide controlled release of the fragrance molecule from the carrier. Examples of pro-fragrances include the Michael addition reaction products of a primary and/or secondary amine compound with an unsaturated ester, acid or nitrile perfume compound. Disclosed amine compounds include polyethyleneimines, such as those commercially available under the “Lupasol” trade name. Another example of a pro-fragrance comprises the reaction product of a primary and/or secondary amine compound with a combination of a perfume ketone component and a high boiling point perfume aldehyde component. The resulting product is said to exhibit a multi-odor benefit to surfaces with which it has been contacted. Further examples of known pro-fragrances that have been said to provide laundry detergent compositions that impart a long-lasting freshness or clean scent to fabrics include ketals and acetals that release fragrance alcohols by hydrolysis of an orthoester.
Various publications have suggested the use of dendrimers as carriers for encapsulating fragrance components. Dendrimers are extremely regular in structure and mono-disperse (i.e., have essentially a single molecular weight without any significant variance).
While the use of pro-fragrances has provided some improvement in delaying the release of the more volatile and/or more soluble fragrance components, it would be desirable to achieve better control of adhesion or substantivity of fragrance molecules to specific substrates, such as textiles, skin, hair, etc., and be able to activate time release over a desired prolonged period. Further, in other cases, it would also be desirable to provide better control of the solubility of fragrance conjugates in liquid media, such as water during washing and/or rinsing cycles. There is also a broader need for developing perfume delivery systems for various consumer products to provide delayed or controlled release of fragrance molecules from substrates, such as skin, hair and textiles.